Model Submission Guidelines

Updated: April 1, 2022

Very Simple Model Content Standard

Building and Bridge models in the BPDA's city model collection are managed in a geographical database that treats models as singular objects associated with attributes. In this context, models do not have any subdivisions such as Layers or nested groups. This makes the model collection simple to manage without much need for a detailed specification or normalization of model organization. Building models are traingulated mesh objects representing the exterior shell of the building.

Model Level of Detail

Here are some additional guidelines for model geometry level of detail:

• If a project has multiple buildings or construction / permitting phases it is best if these are separated into individual .OBJ files.
• If a building is separated into separate functional spaces that can be visually distinguished from the outside, like parking structures, these can be submitted as individual OBJ files but this is not a requirement.
• Our preferred level of detail is LOD 3.0 (See our Level of Detail dictionary) Which may potentially represent over hanging elements like porticos and entryways. If parts of the building protrude beyond the vertical facade by more than a foot and are more than a foot tall, they may be included.
• Window openings should not be cut out or indented.
• The building model may be divided into stories.
• Representing below-ground portions of the building is OK.
• If your building is attached to other buildings, it would be helpful to represent the attached buildings with discrete geometry. .
• If your project has involved making improvements to the models of other buildings in the neighborhood, it would be great to have those, too!

Wavefront Object Format

Use your modeling tool to export a Wavefront Object (.OBJ) format model with the following properties:

• Triangulate all faces (no parametric curves please)
• Model axis orientation: Z Up, Y Forward.
• All faces should have a plain white material that is flat-shaded. Export materials withthe model. This will create a .MTL file that accompanies the .OBJ model file.
• Do not include faces that have both sides exposed. Expect all faces to be invisible when viewd from the wrong side.
• If your model uses materials and or textures, we would be happy to have these, although at this time, our workflow has to remove these. We will keep your textured model in the archive.

Context and Geo-Location

The BPDA has developed a tiling and coordinate referencing scheme that bridges between design tools and GIS. The BPDA uses this coordinate frame for exporting its detailed base models that will be convenient for situating your model. The Tile Grid and Coordinate System page provides the tile referencing grid in many popular 3D formats.

Watch the video demonstration of using the metro3D tile grid to coordinate exchange of models between the BPDA's model collection and your project models. This technique allows you to keep whatever local site origin you might be using.

Preferred:

If it is possible for you to submit your model using our Metro Boston 3D coordinate referencing system, that would be preferred.

Fallback

If it is not possible to export your model using the metro-3D coordinate system, please include a ground-plan reference image as shown in the illustration above. The groundplan should show enough of the edge of pavement in the context area to verify that the model is registered correctly.

Optional Source Material

Our archival system is capable of storing source material, including the plans and elevations and other information that may be part of the project proposal. We can also keep working models -- for example SketchUp or .3DS files. We are Sketchuip Users, so if you have a SketchUp file of your model this may be helpful in case we need to do any trouble-shooting.

On-Going Work In Progress

This submission procedure is a work in progress, so we anticipate problems and hope to work with the development community to make it as easy as possible to participate in building our collaborative open=-source city model!